This invention relates to synchronizing devices for transmissions for automotive vehicles, and more particularly it is concerned with a simple synchronizing device for a manually operated transmission for reversing movement.
Heretofore, no synchronizing device has ever been provided for effecting reversing movement by a transmission used with an automotive vehicle, for example, and when gear shift is swiftly carried out or when gear shift for reversing movement is carried out during low speed forward movement, difficulties have been experienced in smoothly effecting gear shift without producing noise. Nowadays oil of low viscosity is favored and dragging torque has shown a reduction (due to the adoption of roller bearings), so that counter gears or other parts that are normally meshing and rotating at all times do not instantly show a reduction in rotation when the clutch is disengaged while the vehicle remains stationary at neutral shift position. This results in the production of noise during gear shift. Thus the need to provide improvements to the transmission to enable gear shift to be readily and smoothly effected for reversing movement without producing noise has been keenly felt.
In the case of a transmission with a reverse gear train of the normally meshing type, it is possible to readily provide a synchronizing device of the same construction as that for the forward movement. However, such synchronizing device suffers the following two disadvantages.
Firstly, with the reverse gear being in reverse position, a sliding movement of high sliding speed occurs between the reverse gear and the output shaft at the time of forward movement. This makes it necessary to provide means for preventing seizure, thereby increasing cost. Secondly, since the reverse idler gear and the reverse gear are in meshing engagement with each other at all times, noise is produced at neutral position and efficiency is lowered. Moreover, equivalent inertia moment increases when speed change is effected in forward movement, thereby giving an unpleasant feel to the driver in gear shift.
In view of these problems, it is desirable, generally speaking, to adopt a reverse gear train of the selective sliding type in which the reverse idler gear or the reverse gear is selectively moved in sliding movement. However, in view of the construction of this type of reverse gear train, difficulties are encountered in additionally mounting constituent elements of a synchronizing device, such as a synchronizer ring, a shifting key, etc.